This invention relates to sampling apparatus and more particularly to apparatus for obtaining a sample from a specimen of blood or the like and for delivering the sample to means for analyzing it, such as the blood cell counter sold under the trademark "Coulter Counter" Model S by Coulter Electronics, Inc. of Hialeah, Florida, which is used in hospital and commercial laboratories to conduct various tests on whole blood.
Preparatory to analysis, a sample of whole blood is drawn from a patient and typically stored under negative pressure (i.e., a pressure less than atmospheric) in a glass tube with a rubber stopper, such as the type sold under the trade designation "Vacutainer" by Becton-Dickenson and Company of East Rutherford, New Jersey. The blood in this tube is gently and carefully mixed to obtain an even distribution of blood cells and then a sample of the blood is withdrawn for analysis. Heretofore, this has been accomplished in various ways, such as by means of separate mixing and sampling devices or by a device as described in my U.S. Pat. No. 4,120,662.
The specimen sampling apparatus described in this U.S. patent mixes the contents of a series of specimen tubes and delivers them sequentially to a sampling station where a needle, which is connected via a conduit to the intake of a suitable analyzer such as a "Coulter Counter", penetrates the rubber stopper for aspiration of a specimen sample from the tube into the needle and thence through the conduit to the analyzer. However, inasmuch as the contents of the tube are typically under a negative pressure, aspiration of a specimen sample from the tube has presented a problem in that certain analyzers, such as the "Coulter Counter", are unable without modification to develop a negative pressure sufficient to draw a sample from the tube. This problem could be overcome by making major modifications to the analyzer but this would be expensive and complicated.
The contamination of one specimen with particles or cells from another has also presented a problem in prior art sampling apparatus. For sampling apparatus generally in the field of this invention, reference may be made to U.S. Pat. Nos. 3,935,073 and 3,676,679.